1. Field of the Invention:
The present invention relates to a glass sheet bending apparatus for bending a glass sheet at a processing stage in a heating furnace. Particularly, it relates to an improvement in a glass sheet bending apparatus suitable for deep-bending a side of a glass sheet.
2. Discussion of the Background:
There has been known the so-called a horizontal furnace pressing system as a system for bending a glass sheet (Japanese Unexamined Patent Publication 132528/1986). In such system, a glass sheet is heated at a temperature of about 200.degree. C.-650.degree. C. at a bend-processing stage in a heating furnace to bend it into a given curved form; the curved glass sheet is transferred to a cooling stage outside the heating furnace; cooling air is blasted to the curved glass sheet at the cooling stage to temper it, and then the tempered curved glass sheet is removed.
In the above-mentioned system wherein a glass sheet is bent at a high temperature in the heating furnace, it is possible to bend the glass sheet to have a complicated shape because the glass sheet is easily deformed under a high temperature condition in comparison with a system that a glass sheet is bent outside a heating furnace. Further, the system is advantageous in that since the glass sheet is bent in the heating furnace, reduction in temperature is small during the bending operation in comparison with the system that the bending operation is carried out outside the heating furnace. Accordingly, when the glass sheet after bending is subjected to a cooling operation to temper it, the initial temperature can be increased to thereby be able to give a sufficient strength.
There is a publication of, for instance, Japanese Unexamined Patent Publication 178329/1985 which discloses a conventional glass sheet bending apparatus used for the horizontal furnace pressing system. Such bending apparatus is constituted in such a manner as that shown in FIG. 22, a conveyor 3 is arranged in a heating furnace 2 to transfer a glass sheet 1 to a bending stage ST while keeping its horizontal posture; a vacuum suction type mold 4 having a shaping surface which corresponds to the shape of the glass sheet 1 to be shaped is disposed so as to be vertically movable at a place corresponding to the bend-processing stage ST; a lift jet device 5 is disposed below the bend-processing stage ST to blow up an air stream; and a press ring 6 is arranged in the heating furnace 2 adjacent to the bend-processing stage ST so as to be capable of being forwarded and retracted, whereby the glass sheet 1 is bent in the bend-processing stage ST. As the pressing ring 6, there is used, for instance, one comprising a fixed press ring portion 6a having a radius of curvature corresponding to a generally curved surface 4a in the mold 4 and a movable press ring portion 6b having a radius of curvature corresponding to a deep-bending surface 4d in the mold 4 which is connected to the side portion of the fixed press ring portion 6a by a hinge 7.
In the glass sheet bending apparatus, when a heated glass sheet 1 in a flat shape is positioned on the bend-processing stage ST, the mold 4 is descended onto the glass sheet 1, and then air is blown from the lift jet in association with a sucking action by the mold 4. Then, the glass sheet 1 is temporarily shaped on the generally curved surface 4a of the mold 4. The mold 4 is ascended while it keeps the glass sheet 1 thereon. Then, the press ring 6 is forwarded from its waiting position to the bend-processing stage ST so that the movable press ring portion 6b of the press ring 6 presses the side of the glass plate 1 onto the deep-bending surface 4b of the mold 4. As a result, the glass sheet 1 is finally shaped so as to have the finally shaped configuration.
However, when the side portion of the glass sheet 1 is bent by the above-mentioned conventional glass sheet bending apparatus, there is caused relative slide-contact between the movable press ring portion 6d and the side portion of the glass sheet 1 because the radius of curvature of the deep-bending surface 4b is relatively large. Accordingly, scratches may be result in the side portion of the glass sheet 1 to which the movable press ring portion 6d is in a contact resulting in reduction of the quality of the shaped glass sheet 1.